Field of the Invention
The present invention relates to: a method for producing a metal element for a continuously variable transmission, in which the metal element is produced by, using a mold, press forming and punching out a band-shaped metal element material having a constant section; and a metal element for a continuously variable transmission produced by the method.
Description of the Related Art
With regard to a method for producing a metal element used for a metal belt of a belt type continuously variable transmission, Japanese Patent No. 4132820 has made known an arrangement in which a metal element material that is roughly molded into a shape close to a shape of the metal element product is pressed using a mold formed from a main punch and a counterpunch so as to complete molding, thus enhancing precision of a shape in a vicinity of a rocking edge of the metal element while ensuring durability of the mold.
Furthermore, International Publication No. WO2014/196254A1 has made known an arrangement in which a position of a rocking edge of a metal element used for a metal belt of a belt type continuously variable transmission is made to coincide with a front edge position of a saddle face, which is a radially outer end position of a front face of a body part of the metal element, and a positional relationship in a fore-and-aft direction of saddle faces of adjacent metal elements is thus maintained constant when the adjacent metal elements swing relative to each other with the rocking edge as a fulcrum, thereby preventing frictional loss from occurring between the saddle face and a metal ring assembly.
Moreover, when a metal element used for a metal belt of a belt type continuously variable transmission is produced by punching out a band-shaped metal plate using a mold, in order to avoid problems of a material being stretched by shear load accompanying punching out, a phenomenon (rollover) of one end part of a sheared face of a rocking edge being rounded due to plastic deformation, and it not being possible to obtain a sharp rocking edge, Japanese Patent Application Laid-open No. 2013-130204 has made known an arrangement in which a metal element having a sharp rocking edge is produced by punching out as a second element a part of the metal element that includes a rocking edge, and joining the second element to a first element forming a main body part of the metal element such that, among opposite parts of the sheared section, a sharp end part that has no rollover becomes the rocking edge.
In the arrangement described in Japanese Patent No. 4132820, as described in detail in the “DESCRIPTION OF THE PREFERRED EMBODIMENTS” section of the present specification, when a metal element is press formed using a mold, since a plate thickness of a body part positioned on a radially inner side of the metal element is slightly smaller than a plate thickness of an ear part positioned on a radially outer side, when a large number of metal elements come into intimate contact with each other in a chord portion of a metal belt when it is wound around a drive pulley and a driven pulley to transmit a driving force, the chord portion of the metal belt curves toward the radially outer side due to the difference in plate thickness, and there is a possibility that the efficiency of transmission of the driving force will be degraded.
Furthermore, in the arrangement described in Japanese Patent No. 4132820, when press forming the metal element from the metal element material using the mold, since the amount of material of the metal element material that is pushed aside by the mold is large, there is a possibility that the pressing load required will become large or the durability of the mold will be degraded.
Moreover, in the arrangement described in Japanese Patent Application Laid-open No. 2013-130204, since the metal element is assembled from the first element and the second element, which are two separate members, there is a problem that the number of components increases and the production cost rises.